The present invention relates to switch mechanisms and particularly to a switch mechanism of small size having an extended useful life, and suitable for assembly by automated equipment.
It is well-known that alternating current switches constitute the principle form of switches employed in the switching of current to lighting fixtures and in other branch cirucit applications within residences and other buildings. The branch circuit within a home and in many other buildings normally carries 15 to 20 amperes. It usually extends from the service entrance where the electric power enters the building. Normally such a branch cirucit is protected by a single fuse or circuit breaker at the service entrance of the building.
The normal load on such a branch cirucit is of the order of 15 amperes or less, particularly where the load is lighting fixtures such as are conventionally controlled by AC switches within conventional residences. Because of the very large number of such switches in homes and other buildings, it is highly desirable that these switches by manufactured at relatively low cost although the switch must nevertheless provide fully reliable switching action and must be fully capable of performing the switching operation involving the on-off control of the 15 amperes of power at the conventional 120 volts. The Underwriters' Laboratory normally makes a requirement that such switches for use in home applications be capable of controlling some 30,000 on-off switching operations. This testing by Underwriters' Laboratories is done under overload conditions according to Standard Test Number UL20. Further, it is known that it is desirable that a switch have not only high reliability and extended life but also be relatively small in size. The small size is desirable because it is installed in a normal wall box which may measure 3 inches (7.62 cm.) in height by 2 inches (5.08 cm.) in width and 1-1/2 (3.81 cm.) to 2 (5.08 cm.) inches in depth. Further there are shallow wall boxes for installation with wall paneling and the like which have a depth of only 1 inch. Accordingly there is a distinct advantage in having a reliable AC switch which will occupy a fairly small part of this wall box enclosure so that there will be adequate room in the box for the lengths of wire stored there due to the needs associated with conventional wiring practice as well as wire nuts and other elements employed in connection with properly wiring a switch to control a load in a branch circuit.
Another feature which is sought in AC switches is a low manufacturing cost and this cost is of course made up of a material cost and labor cost. Where the switch has relatively low material content and where the switch is readily assembled the manufacturing cost of the overall device can also be relatively low. The cost of assembly can be greatly benefitted if the structure of the switch is such that it can be assembled by automated equipment. However, the building of an automatable switch requires that the switch structure itself be fairly simple and that the individual parts be easy to assemble in a reliable fashion. The smaller the number of parts and the simpler the individual parts to make up a switch, the greater is the likelihood that a machine to assemble the switch can be designed and can be produced at a reasonable cost.
Accordingly, it will be seen from the foregoing that the combination of properties desirable in a switch is relatively hard to achieve inasmuch as some of the criteria of a switch contradict others and achievement of the overall favorable performance is a matter of some technical difficulty. For example, where a switch is to be reliable it must have a fairly controlled dimensional spacing of its various parts and particularly of the parts which are to perform the movement which results in the switching action. However, where the switch and the elements of the switch are of simple design and thus suitable for automated assembly, it is not easy to achieve the close dimensional control of the moving parts such as will ensure reliable switching action. The automated assembly of a switch is most easily achieved where the dimensions of the product and of the component parts are precisely controlled, but such control is difficult where the component parts themselves are quite simple and where their assembly is also quite simple as by reliance upon gravity.
A number of switch articles which may have one or more of the features as above noted have been known heretofore and illustrative switches are those taught by U.S. Pat. Nos. 2,578,494, 2,962,572, and 3,165,614. Other switches having still other features and combinations of features such as those shown in U.S. Pat. Nos. 3,283,105 and 3,030,479 are also known in the switch art. However, these reference patents do not contain a unique combination of all of the features discussed above.
There is also a general outward resemblance between a switch described in U.S. Pat. No. 3,532,846 and the switch product taught in this application both of which are assigned to the same assignee. However, the switch of U.S. Pat. No. 3,532,846 does not have the same internal elements as the switch structure taught below nor does it have the same features, such as automatability, or functional properties as the switch structure taught and claimed herein.